The Lord (Visnu) incarnates Himself in each and every one of them and in each and every type of living society
SB Canto 1
Thus the Lord of the universes maintains all planets inhabited by demigods, men and lower animals. Assuming the roles of incarnations, He performs pastimes to reclaim those in the mode of pure goodness.
There are innumerable material universes, and in each and every universe there are innumerable planets inhabited by different grades of living entities in different modes of nature. The Lord (Viṣṇu) incarnates Himself in each and every one of them and in each and every type of living society. He manifests His transcendental pastimes amongst them just to create the desire to go back to Godhead. The Lord does not change His original transcendental position, but He appears to be differently manifested according to the particular time, circumstances and society.
Sometimes He incarnates Himself or empowers a suitable living being to act for Him, but in either case the purpose is the same: the Lord wants the suffering living being to go back home, back to Godhead. The happiness which the living beings are hankering for is not to be found within any corner of the innumerable universes and material planets. The eternal happiness which the living being wants is obtainable in the kingdom of God, but the forgetful living beings under the influence of the material modes have no information of the kingdom of God. The Lord, therefore, comes to propagate the message of the kingdom of God, either personally as an incarnation or through His bona fide representative as the good son of God. Such incarnations or sons of God are not making propaganda for going back to Godhead only within the human society. Their work is also going on in all types of societies, amongst demigods and those other than human beings.